Amy C. Degnim, MD

Both nuclei retain continuity with the central grey matter at this level erectile dysfunction pills canada cheap vivanza 20 mg overnight delivery, but this is subsequently lost erectile dysfunction treatment abu dhabi purchase vivanza canada. First-order gracile and cuneate fascicular fibres erectile dysfunction urban dictionary vivanza 20 mg without a prescription, which have ascended ipsilaterally and uninterrupted from their origin in the spinal cord erectile dysfunction drugs history discount vivanza online, synapse on neurones in their respective nuclei erectile dysfunction gnc products discount vivanza 20 mg with mastercard. Second-order axons emerge from the nuclei as internal arcuate fibres, at first curving ventrolaterally around the central grey matter and then ventromedially between the trigeminal spinal tract and the central grey matter. The lemniscal decussation is located dorsal to the pyramids and ventral to the central grey matter. The medial lemniscus ascends from the lemniscal decussation on each side as a flattened tract near the median raphe. As the tracts ascend, they increase in size because fibres join from upper levels of the decussation. Corticospinal fibres are ventral, and the medial longitudinal fasciculus and tectospinal tract are dorsal. Fibres are rearranged in the decussation, so that those from the nucleus gracilis come to lie ventral to those from the nucleus cuneatus. Above Transverse Section of the Medulla at the Level of the Decussation of the Medial Lemniscus 158 Chapter 10 / Brain Stem Tentorium cerebelli Trochlear nerve Tentorial notch Median sulcus of fourth ventricle Trigeminal nerve Transverse dural venous sinus Facial and vestibulocochlear nerves Glossopharyngeal, vagus and accessory nerves Accessory nerve, spinal root Vertebral artery First cervical (suboccipital) nerve Atlas, posterior arch Hypoglossal nerve Posterior spinal artery Digastric, posterior belly Atlas, transverse process Spinal accessory nerve Second cervical spinal ganglion Vagus nerve Internal jugular vein Sternocleidomastoid Superior cervical sympathetic ganglion Dura mater Third cervical nerve dorsal ramus Denticulate ligament Spinal accessory nerve Vagus nerve (displaced medially) Common carotid artery Vertebral artery. On the left, the foramina transversaria of the atlas and the third, fourth and fifth cervical vertebrae have been opened to expose the vertebral artery. At this level, medial lemniscal fibres show a laminar somatotopy on a segmental basis, in that fibres from C1 to S4 spinal segments are segregated sequentially from medial to lateral. The latter progressively incline dorsally and enter the inferior cerebellar peduncle at a higher level. One is dorsolateral to the pyramid, and the other is medial to it and near the median plane. These are parts of the precerebellar medial accessory olivary nucleus, described with the inferior olivary nuclear complex. Precerebellar nuclei of the vestibular, pontine and reticular system are described in Chapter 13. Transverse Section of the Medulla at the Caudal End of the Fourth Ventricle A transverse section level with the lower end of the fourth ventricle shows some new features, along with most of those already described. The total area of grey matter is increased by the presence of the large olivary nuclear complex and nuclei of the vestibulocochlear, glossopharyngeal, vagus and accessory nerves. A smooth, oval elevation-the olive-lies between the ventrolateral and dorsolateral sulci of the medulla. It is formed by the underlying inferior olivary complex of nuclei and lies lateral to the pyramid, separated from it by the ventrolateral sulcus and emerging hypoglossal nerve fibres. The roots of the facial nerve emerge between its rostral end and the lower pontine border, in the cerebellopontine angle. The arcuate nuclei are curved, interrupted bands, ventral to the pyramids, and are said to be displaced pontine nuclei. Anterior external arcuate fibres and those of the striae medullares are derived from them. They project mainly to the contralateral cerebellum through the inferior cerebellar peduncle. It has a longitudinal medial hilum and is surrounded by myelinated fibres that form the olivary amiculum. It contains (sequentially from medial to lateral) the hypoglossal nucleus, dorsal vagal nucleus, nucleus solitarius and caudal ends of the inferior and medial vestibular nuclei. Pineal body Superior colliculus Inferior colliculus Inferior quadrigeminal brachium Medial geniculate body Superior medullary velum Lateral lemniscus Superior cerebellar peduncle Middle cerebellar peduncle Corona radiata Pulvinar Superior quadrigeminal brachium Lateral geniculate body Lentiform complex Trochlear nerve Optic tract Base of cerebral peduncle Oculomotor nerve Dorsolateral sulcus Roots of spinal accessory nerve Olive Pyramid Roots of vagus and glossopharyngeal nerves Pons Trigeminal nerve (sensory and motor roots). Dorsal median sulcus Nucleus gracilis Internal arcuate fibres Spinal tract of trigeminal nerve Spinal nucleus of trigeminal nerve Dorsal spinocerebellar tract Fasciculus gracilis Dorsal intermediate sulcus Fasciculus cuneatus Nucleus cuneatus Central canal Ventral spinocerebellar tract Decussation of lemnisci Anterior external arcuate fibres Reticular formation Medial accessory olivary nucleus Olivary complex Pyramid Medial lemniscus Ventral median fissure. The tractus solitarius and its associated circumferential nucleus solitarius extend throughout the length of the medulla. The tract is composed of general visceral afferents from the vagus and glossopharyngeal nerves. The nucleus and its central connections with the reticular formation subserve the reflex control of cardiovascular, respiratory and cardiac functions. The rostral fibres of the tract consist of gustatory fibres from the facial, glossopharyngeal and vagal nerves that project to the rostral pole of the nucleus solitarius, which is sometimes referred to as the gustatory nucleus. The medial longitudinal fasciculus, a small, compact tract near the midline and ventral to the hypoglossal nucleus, is continuous with the ventral vestibulospinal tract. At this medullary level it is displaced dorsally by the pyramidal and lemniscal decussations. Neurological examination reveals downbeat nystagmus with the eyes in the primary position, amplified by down-gaze; dysmetria of the lower extremities with heel-to-shin testing; and hyperreflexia in both lower extremities. Discussion: Downbeat nystagmus consists of a rapid downbeat motion of the eyes followed by a slower upward movement. This is usually present with the eyes in the primary position, but at times it is so subtle that it can be seen only with ophthalmoscopy. The amplitude of the movements is usually increased by down-gaze and sometimes by horizontal gaze to either side. It is characteristically associated with conditions involving the medulla oblongata, particularly at the level of the craniocervical junction. These conditions include Arnold­Chiari malformation, as is the case in this woman. Within 2 days, the sensory loss spread to involve the entire left arm, then the left leg; at that point he developed an increasingly severe left hemiparesis. Examination demonstrated a flaccid left hemiparesis with exaggerated reflex activity bilaterally. There was reduction in vibratory sense on the left side; sensation was otherwise normal. There was mild wasting on the left side of the tongue, with fasciculation and the left sternomastoid muscle was slightly atrophic. The neuro-anatomic structures involved include the corticospinal tracts causing contralateral hemiparesis, the medial lemniscus leading to impaired posterior column sensibility, the accessory nerve causing mild atrophy of the sternomastoid muscle, and the hypoglossal nerve producing atrophy of the tongue with fasciculations. This syndrome is rare, and variably described; in a number of cases, palatal weakness has been observed. The spinocerebellar, spinotectal, vestibulospinal, rubrospinal and lateral spinothalamic (spinal lemniscal) tracts all lie in the ventrolateral area of the medulla at this level. The tracts are limited dorsally by the spinal trigeminal nucleus and ventrally by the pyramid. Numerous islets of grey matter are scattered centrally in the ventrolateral medulla, an area intersected by nerve fibres that run in all directions. This is the reticular formation, which exists throughout the medulla and extends into the pontine tegmentum and midbrain. Pyramidal Tract Each pyramid contains descending corticospinal fibres, derived from the ipsilateral cerebral cortex, which have traversed the internal capsule, midbrain and pons. Approximately 70% to 90% of the axons leave the pyramids in successive bundles, crossing in and deep to the ventral median fissure as the pyramidal decussation. In the rostral medulla, fibres cross by inclining ventromedially, whereas more caudally, they pass dorsally, decussating ventral to the central grey matter. The decussation is orderly, with fibres destined to end in the cervical segments crossing first. They continue to pass dorsally as they descend, reaching the contralateral spinal lateral funiculus as the crossed lateral corticospinal tract. Most uncrossed corticospinal fibres descend ventromedially in the ipsilateral ventral funiculus, as the ventral corticospinal tract. A minority run dorsolaterally to join the lateral corticospinal tracts as a small uncrossed component. In the pyramids the arrangement is like that at higher levels, in that the most lateral fibres subserve the most medial arm and neck movements. Similar somatotopy is ascribed to the lateral corticospinal tracts within the spinal cord. The nuclei gracilis and cuneatus are part of the pathway that is considered the major route for discriminative aspects of tactile and locomotor. The upper regions of both nuclei are reticular and contain small and large multipolar neurones with long dendrites. The lower regions contain clusters of large, round neurones with short and profusely branching dendrites. Upper and lower zones differ in their connections, but both receive terminals from the dorsal spinal roots at all levels. Dorsal funicular fibres from neurones in the spinal grey matter terminate only in the superior, reticular zone. Variable ordering and overlap of terminals, on the basis of spinal root levels, occur in both zones. The lower extremity is represented medially, the trunk ventrally and the digits dorsally. There is modal specificity; that is, lower levels respond to low-threshold cutaneous stimuli, and upper reticular levels respond to inputs from fibres serving receptors in the skin, joints and muscles. Its middle zone contains a large pars rotunda, in which rostrocaudally elongated, medium-sized neurones are clustered between bundles of densely myelinated fibres. The reticular poles of its rostral and caudal zones contain scattered but evenly distributed neurones of various sizes. The nucleus receives the lateral fibres of the fasciculus cuneatus, carrying proprioceptive impulses from the upper limb (which enter the cervical spinal cord rostral to the thoracic nucleus). A group of neurones, called nucleus Z, has been identified in animals between the upper pole of the nucleus gracilis and the inferior vestibular nucleus and is said to be present in the human medulla. Its input is probably from the dorsal spinocerebellar tract, which carries proprioceptive information from the ipsilateral lower limb, and it projects through internal arcuate fibres to the contralateral medial lemniscus. The trigeminal sensory nucleus receives the primary afferents of the trigeminal nerve. It is a large nucleus and extends caudally into the cervical spinal cord and rostrally into the midbrain. The principal and largest division of the nucleus is located in the pontine tegmentum. On entering the pons, the fibres of the sensory root of the trigeminal nerve run dorsomedially toward the principal sensory nucleus, which is situated at this level. Before reaching the nucleus, approximately 50% of the fibres divide into ascending and descending branches; the others ascend or descend without division. The descending fibres, 90% of which are less than 4 µm in diameter, form the spinal tract of the trigeminal nerve, which reaches the upper cervical spinal cord. Fibres from the ophthalmic root lie ventrolaterally, those from the mandibular root lie dorsomedially and the maxillary fibres lie between them. The tract is completed on its dorsal rim by fibres from the sensory roots of the facial, glossopharyngeal and vagus nerves. The detailed anatomy of the trigeminospinal tract excited early clinical interest because it was recognized that dissociated sensory loss could occur in the trigeminal area. There are conflicting opinions about the termination pattern of fibres in the spinal nucleus. According to this view, ophthalmic fibres are ventral and descend to the lower limit of the first cervical spinal segment, maxillary fibres are central and do not extend below the medulla oblongata and mandibular fibres are dorsal and do not extend much below the mid-medullary level. The results of section of the spinal tract in cases of severe trigeminal neuralgia support this distribution. To include the mandibular area, it was necessary to section at the level of the obex. More recently, it has been proposed that fibres are arranged dorsoventrally within the spinal tract. There appear to be sound anatomical, physiological and clinical reasons for believing that all divisions terminate throughout the whole nucleus, although the ophthalmic division may not project fibres as far caudally as the maxillary and mandibular divisions do. Fibres from the posterior face (adjacent to C2) terminate in the lower (caudal) part, whereas those from the upper lip, mouth and nasal tip terminate at a higher level. This can give rise to a segmental (cross-divisional) sensory loss in syringobulbia. Fibres of the glossopharyngeal, vagus and facial nerves subserving common sensation (general visceral afferent) form a column dorsally within the spinal tract of the trigeminal nerve and synapse with cells in the lowest part of the spinal trigeminal nucleus. Consequently, operative section of the dorsal part of the spinal tract results in analgesia that extends to the mucosa of the tonsillar sinus, the posterior third of the tongue and adjoining parts of the pharyngeal wall (glossopharyngeal nerve) and the cutaneous area supplied by the auricular branch of the vagus. Other afferents that reach the spinal nucleus are from the dorsal roots of the upper cervical nerves and from the sensorimotor cortex. The spinal nucleus is considered to consist of three parts: the subnucleus oralis (which is most rostral and adjoins the principal sensory nucleus), the subnucleus interpolaris and the subnucleus caudalis (which is the most caudal part and is continuous below with the dorsal grey column of the spinal cord). The structure of the subnucleus caudalis is different from that of the other trigeminal sensory nuclei. It has a structure analogous to that of the dorsal horn of the spinal cord, with a similar arrangement of cell laminae, and it is Pyramid Trigeminal Sensory Nucleus Uncrossed fibres Decussation of the pyramids Lateral corticospinal tract Ventral corticospinal tract. There is a somatotopic pattern of termination of cutaneous inputs from the upper limb on the cell clusters of the pars rotunda. The gracile and cuneate nuclei serve as relays between the spinal cord and higher levels. Primary spinal afferents synapse with multipolar neurones in the nuclei to form the major nuclear efferent projection. Descending afferents from the somatosensory cortex reach the nuclei through the corticobulbar tracts and appear to be restricted to the upper, reticular zones. Because these afferents both inhibit and enhance activity, the nuclear region is clearly one of sensory modulation.

The middle part of the cranial base is completed by the petrous processes of the two temporal bones erectile dysfunction specialist doctor purchase vivanza canada, which pass from the lateral sides of the base of the skull toward the site of union of the sphenoid and occipital bones erectile dysfunction causes prescription drugs vivanza 20 mg discount. Each petrous process meets the basilar part of the occipital bone at a petrooccipital suture alcohol and erectile dysfunction statistics purchase cheapest vivanza and vivanza, which is deficient posteriorly at the jugular foramen erectile dysfunction surgery cost order genuine vivanza line. The petrosphenoidal suture and the groove for the pharyngotympanic tube lie between the petrous process and the infratemporal surface of the greater wing of the sphenoid erectile dysfunction medication options discount vivanza 20 mg with amex. The apex of the petrous process does not meet the spheno-occipital suture, and the deficit produced is called the foramen lacerum. Each pterygoid process of the sphenoid bone bears medial and lateral pterygoid plates separated by a pterygoid fossa. Anteriorly, the plates are fused, except below, where they are separated by the pyramidal process of the palatine bone. Laterally, the pterygoid plates are separated from the posterior maxillary surface by the pterygomaxillary fissure, which leads into the pterygopalatine fossa. The posterior border of the medial pterygoid plate is sharp and bears a small projection near the midpoint, above which it is curved and attached to the pharyngeal end of the pharyngotympanic tube. Above, the medial pterygoid plate divides to enclose the scaphoid fossa; below, it projects as a slender pterygoid hamulus, which curves laterally and is grooved anteriorly by the tendon of tensor veli palatini. The lateral pterygoid plate projects posterolaterally, and its lateral surface forms the medial wall of the infratemporal fossa. Superiorly and laterally, the pterygoid process is continuous with the infratemporal surface of the greater wing of the sphenoid bone, which forms part of the roof of the infratemporal fossa. This surface forms the posterolateral border of the inferior orbital fissure and bears an infratemporal crest associated with the origin of the upper part of the lateral pterygoid. The infraorbital and zygomatic branches of the maxillary nerve and accompanying vessels pass through the inferior orbital fissure. Laterally, the greater wing of the sphenoid bone articulates with the squamous part of the temporal bone. Features associated with the pterygoid plate region can be assessed radiographically. A thin-walled depression in the temporal bone, the mandibular fossa, can be inspected when the mandible is removed; in front of this, the zygomatic arch extends laterally. A distinct ridge, the articular eminence, is anterior to the fossa, and three fissures can be distinguished behind it. The squamotympanic fissure extends from the spine of the sphenoid, between the mandibular fossa and the tympanic plate of the temporal bone, and curves up the anterior margin of the external acoustic meatus. A thin wedge of bone forming the inferior margin of the tegmen tympani lies within the fissure and divides the squamotympanic fissure into petrotympanic and petrosquamous fissures. The petrotympanic fissure transmits the chorda tympani branch of the facial nerve from the skull into the infratemporal fossa. The foramen lacerum is bounded in front by the body and adjoining roots of the pterygoid process and greater wing of the sphenoid bone, posterolaterally by the apex of the petrous part of the temporal bone and medially by the basilar part of the occipital bone. A large, almost circular foramen, the carotid canal, lies behind and posterolateral to the foramen lacerum in the petrous part of the temporal bone. The internal carotid artery enters the skull through this foramen, ascends in the carotid canal and turns anteromedially to reach the posterior wall of the foramen lacerum. It ascends through the upper end of the foramen lacerum with its venous and sympathetic nerve plexuses. Meningeal branches of the ascending pharyngeal artery and emissary veins from the cavernous sinus also traverse the foramen lacerum. In life, the lower part of the foramen lacerum is partially occluded by cartilaginous remnants of the developmental chondrocranium. The pterygoid canal can be seen on the base of the skull at the anterior margin of the foramen lacerum, above and between the pterygoid plates of the sphenoid bone. It leads into the pterygopalatine fossa and contains the nerve of the pterygoid canal and accompanying blood vessels. The foramen ovale and foramen spinosum lie lateral to the foramen lacerum on the infratemporal surface of the greater wing of the sphenoid bone. The foramen ovale, near the posterior margin of the lateral pterygoid 152 Chapter 9 / Skull plate, transmits the mandibular nerve as well as the lesser petrosal nerve, the accessory meningeal branch of the maxillary artery and an emissary vein that connects the cavernous venous sinus to the pterygoid venous plexus in the infratemporal fossa. Posterolaterally, the smaller and rounder foramen spinosum transmits the middle meningeal artery and a meningeal branch of the mandibular nerve. The irregular spine of the sphenoid projects posterolateral to the foramen spinosum. The medial surface of the spine is flat and forms, with the adjoining posterior border of the greater wing of the sphenoid, the anterolateral wall of a groove that is completed posteromedially by the petrous part of the temporal bone. This groove contains the cartilaginous pharyngotympanic (auditory) tube and leads posterolaterally into the bony portion of the tube lying within the petrous part of the temporal bone. A small foramen, the sphenoidal emissary foramen (of Vesalius), is sometimes found between the foramen ovale and scaphoid fossa. When present, it contains an emissary vein linking the pterygoid venous plexus in the infratemporal fossa with the cavernous sinus in the middle cranial fossa. The zygomaticotemporal foramen passes up and backward from the posterior surface of the zygomatic bone in the anterior wall of the infratemporal fossa. Prominent features are the foramen magnum and associated occipital condyles, jugular foramen, mastoid and styloid processes of the temporal bone, stylomastoid foramen, mastoid notch and squamous part of the occipital bone up to the external occipital protuberance and the superior nuchal lines, hypoglossal canals (anterior condylar canals) and condylar canals (posterior condylar canals). It contains the lower end of the medulla oblongata, the vertebral arteries and the spinal accessory nerve. Anteriorly, the margin of the foramen magnum is slightly overlapped by the occipital condyles, which project down to articulate with the superior articular facets on the lateral masses of the atlas. Each occipital condyle is oval in outline and oriented obliquely so that its anterior end lies nearer the midline. It is markedly convex anteroposteriorly and less so transversely; its medial aspect is roughened by ligamentous attachments. The hypoglossal canal, directed laterally and slightly forward, traverses each condyle and transmits the hypoglossal nerve, a meningeal branch of the ascending pharyngeal artery and an emissary vein from the basilar plexus. A depression, the condylar fossa, lies immediately posterior to the condyle and sometimes contains a (posterior) condylar canal for an emissary vein from the sigmoid sinus. A jugular process joins the petrous part of the temporal bone lateral to each condyle, and its anterior border forms the posterior boundary of the jugular foramen. Laterally, the occipital bone joins the petrous part of the temporal bone anteriorly, at the petro-occipital suture, and the mastoid process of the temporal bone more posteriorly, at the petromastoid suture. The jugular foramen, a large irregular hiatus, lies at the posterior end of the petro-occipital suture between the jugular process of the occipital bone and the jugular fossa of the petrous part of the temporal bone. A number of important structures pass through this foramen: inferior petrosal sinus (anterior); glossopharyngeal, vagus and accessory nerves (midway); internal jugular vein (posterior). A mastoid canaliculus runs through the lateral wall of the jugular fossa and transmits the auricular branch of the vagus nerve. The canaliculus for the tympanic nerve-a branch of the glossopharyngeal nerve in the cavity of the middle ear-lies on the ridge between the jugular fossa and the opening of the carotid canal. A small notch, related to the inferior glossopharyngeal ganglion, may be found medially, on the upper boundary of the jugular foramen (it is more easily identified internally). The stylomastoid foramen lies between the mastoid and styloid processes of the temporal bone on the lateral aspect. A groove, the mastoid notch, lies medial to the mastoid process and gives origin to the posterior belly of the digastric. A mastoid foramen may be present near or in the occipitomastoid suture; when present, it transmits an emissary vein from the sigmoid sinus. It is surrounded inferiorly by the tympanic plate, which partly ensheathes the base of the styloid process. The squamous part of the occipital bone exhibits the external occipital protuberance; supreme, superior and inferior nuchal lines; and the external 17 18. The region is roughened for the attachment of muscles whose primary function is extension of the skull. The floor of the anterior cranial fossa is at the highest level and the floor of the posterior fossa is at the lowest. Anterior Cranial Fossa the anterior cranial fossa is formed at the front and sides by the frontal bone. Its floor contains the orbital plate of the frontal bone, the cribriform plate and crista galli of the ethmoid bone and the lesser wings and anterior part of the body of the sphenoid. Unlike the other cranial fossae, it does not directly communicate with the inferior surface of the cranium; instead, it is related to the roofs of the orbits and the nasal fossae. A perforated plate of bone, the cribriform plate of the ethmoid bone, spreads across the midline between the orbital plates of the frontal bone and is depressed below them, forming part of the roof of the nasal cavity. Olfactory nerves pass from the nasal mucosa to the olfactory bulb of the brain through numerous small foramina in the cribriform plate. Anteriorly, a spur of bone, the crista galli, projects upward between the cerebral hemispheres. A depression between the crista galli and the crest of the frontal bone is crossed by the frontoethmoidal suture and bears the foramen caecum, which is usually a small blind-ended depression but occasionally accommodates a vein draining from the nasal mucosa to the superior sagittal sinus. The anterior ethmoidal nerve enters the cranial cavity where the cribriform plate meets the orbital part of the frontal bone and then passes into the roof of the nose via a small foramen by the side of the crista galli; the nerve grooves the crista galli. The posterior ethmoidal canal, which transmits the posterior ethmoidal nerve and vessels, opens at the posterolateral corner of the cribriform plate and is overhung by the sphenoid bone. The convex cranial surface of the frontal bone separates the brain from the orbit and bears impressions of cerebral gyri and small grooves for meningeal vessels. Posteriorly, it joins the anterior border of the lesser wing of the sphenoid bone, which forms the posterior boundary of the anterior cranial fossa. The lesser wing joins the body of the sphenoid body by two roots that are separated by the optic canal. The frontosphenoid and sphenoethmoidal sutures divide the sphenoid from the adjacent bones. The posterior border of each lesser wing fits the stem of the lateral cerebral sulcus and may be grooved by the sphenoparietal sinus. Above is the inferior surface of the frontal lobe of the cerebral hemisphere, and medial is the anterior perforated substance. Inferiorly, the lesser wing bounds the superior orbital fissure and completes the orbital roof. Each anterior clinoid process gives attachment to the free margin of the tentorium cerebelli and is grooved medially by the internal carotid artery as it leaves the cavernous sinus. It may be connected to the middle clinoid process by a thin osseous bar, completing a caroticoclinoid foramen around the artery. Her clinical abnormalities include a mild contralateral hemiparesis, behavioural change, ipsilateral optic atrophy with contralateral papilloedema and ipsilateral anosmia. Similar symptoms may also appear with other tumours, such as meningioma involving the sphenoid wing. Reduced visual acuity with optic atrophy is due to direct compression of the ipsilateral optic nerve or optic chiasma, whereas papilloedema involving the contralateral optic nerve clearly indicates the presence of increased intracranial pressure, a combination that is uncommon today in light of early diagnostic studies. It is bounded in front by the lesser wings and part of the body of the sphenoid, behind by the superior borders of the petrous part of the temporal bone and the dorsum sellae of the sphenoid and laterally by the squamous parts of the temporal bone, parietal bone and greater wings of the sphenoid. The hollowed-out area is the site of the hypophysial (pituitary) gland and is therefore termed the hypophysial (pituitary) fossa. The area has the shape of a Turkish saddle and is also known as the sella turcica. The anterior edge of the hypophysial fossa is completed laterally by a middle clinoid process. The floor forms the roof of the sphenoidal air sinuses, and the posterior boundary presents a vertical pillar of bone, the dorsum sellae. The superolateral angles of the dorsum sellae are expanded as the posterior clinoid processes. A fold of dura, the diaphragma sella, is attached to the anterior and posterior clinoid processes and roofs the hypophysial fossa. The smooth upper part of the anterior wall of the fossa is the jugum sphenoidale, which is bounded behind by the anterior border of the grooved sulcus chiasmatis, leading laterally to the optic canals. The optic nerve and ophthalmic artery pass through the optic canal, and the optic chiasma usually lies posterosuperior to the sulcus chiasmatis. The cavernous sinus lies lateral to the hypophysial fossa, and the lateral wall of the body of the sphenoid contains a shallow carotid groove related to the internal carotid artery as it ascends from the carotid canal and runs through the cavernous sinus. Laterally, the middle cranial fossa is deep and supports the temporal lobes of the cerebral hemispheres. Anteriorly are the orbits, laterally the temporal fossae and inferiorly the infratemporal fossae. The middle cranial fossa communicates with the orbits by the superior orbital fissures, each bounded above by a lesser wing, below by a greater wing and medially by the body of the sphenoid bone. Each fissure is wider medially and has a long axis sloping inferomedially and forward. Many nerves and vessels pass through it: the oculomotor, trochlear and abducens nerves and the lacrimal, frontal and nasociliary branches of the ophthalmic division of the trigeminal nerve, together with filaments from the internal carotid plexus (sympathetic), the ophthalmic veins, the orbital branch of the middle meningeal artery and the recurrent branch of the lacrimal artery. The foramen rotundum is situated just below and behind the medial end of the superior orbital fissure and leads forward into the pterygopalatine fossa, to which it conducts the maxillary nerve. Behind the foramen rotundum is the foramen ovale, which transmits the mandibular nerve. The foramen spinosum is posterolateral to the foramen ovale and transmits the middle meningeal artery. The latter, with companion veins, ascends lateral to the squamous part of the temporal bone and turns anterolaterally across the sphenosquamosal suture to the greater wing of the sphenoid bone, where it divides into frontal and parietal branches. The frontal branch ascends across the pterion to the anterior part of the parietal bone; at or near the pterion it is often in a bony canal. The parietal branch runs back and up onto the squamous part of the temporal bone, crossing the squamosal suture to gain the parietal bone.

Clearance of propofol from the plasma exceeds hepatic blood flow erectile dysfunction drugs walmart purchase 20 mg vivanza with amex, emphasizing that tissue uptake (possibly into the lungs) erectile dysfunction treatment uk cheap vivanza 20 mg amex, as well as hepatic oxidative metabolism by cytochrome P450 erectile dysfunction usmle order 20 mg vivanza with visa, is important in removal of this drug from the plasma (Table 5-1) impotence symptoms vivanza 20 mg buy otc. Despite the rapid clearance of propofol by metabolism impotence nerve order generic vivanza on-line, there is no evidence of impaired elimination in patients with cirrhosis of the liver. Prompt recovery without residual sedation and low incidence of nausea and vomiting make propofol particularly well suited to ambulatory conscious sedation techniques. In selected Chapter 5 · Intravenous Sedatives and Hypnotics Table 5-1 Comparative Characteristics of Common Induction Drugs Elimination Half-Time (h) Propofol Etomidate Ketamine 0. Increasing metabolic acidosis, lipemic plasma, bradycardia, and progressive myocardial failure has been described. General anesthesia that includes propofol is typically associated with minimal postoperative nausea and vomiting, and awakening is prompt, with minimal residual sedative effects. The incidence of postoperative nausea and vomiting is decreased when propofol is administered, regardless of the anesthetic technique. When administered to induce and maintain anesthesia, it is more effective than ondansetron in preventing postoperative nausea and vomiting. Subhypnotic doses of propofol that are effective as an antiemetic do not inhibit gastric emptying and propofol is not considered a prokinetic drug. Propofol decreases the prevalence of wheezing after induction of anesthesia and tracheal intubation in healthy and asthmatic patients. However, a formulation of propofol that uses metabisulfite as a preservative may cause bronchoconstriction in asthmatic patients. Cortical somatosensory evoked potentials as used for monitoring spinal cord function are not significantly modified in the presence of propofol alone but the addition of nitrous oxide or a volatile anesthetic results in decreased amplitude. The relaxation of vascular smooth muscle produced by propofol is primarily due to inhibition of sympathetic vasoconstrictor nerve activity. Peripheral vascular effects of thiopen, tal and propofol in humans with artificial hearts. The blood pressure effects of propofol may be exaggerated in hypovolemic patients, elderly patients, and patients with compromised left ventricular function. Profound bradycardia and asystole after administration of propofol have been described in healthy adult patients, despite prophylactic anticholinergics (risk of bradycardia-related death during propofol anesthesia has been estimated to be 1. Treatment of propofol-induced bradycardia may require treatment with a direct -agonist such as isoproterenol. Propofol produces dose-dependent depression of ventilation, with apnea occurring in 25% to 35% of patients after induction of anesthesia with propofol. Opioids administered with the preoperative medication enhance ventilatory depressant. Propofol does not normally affect hepatic or renal function as reflected by measurements of liver transaminase enzymes or creatinine concentrations. Prolonged infusions of propofol may also result in excretion of green urine, reflecting the presence of phenols in the urine (does not alter renal function). Urinary uric acid excretion is increased after administration of propofol and may manifest as cloudy urine when the uric acid crystallizes in the urine under conditions of low pH and temperature (not considered to be detrimental). Propofol is associated with significant decreases in intraocular pressure that occur immediately after induction of anesthesia and are sustained during tracheal intubation. Propofol inhibits platelet aggregation that is induced by proinflammatory lipid mediators including thromboxane A2 and platelet-activating factor. Patients who develop evidence of anaphylaxis on first exposure to propofol may have been previously sensitized to the diisopropyl radical, which is present in many dermatologic preparations. Anaphylaxis to propofol during the first exposure to this drug has been observed, especially in patients with a history of other drug allergies, often to neuromuscular blocking drugs. Lactic acidosis ("propofol infusion syndrome") has been described in pediatric and adult patients receiving prolonged high-dose infusions of propofol (75 g/kg/ minute) for longer than 24 hours. The mechanism for sporadic propofol-induced metabolic acidosis is unclear but may reflect poisoning (cytopathic hypoxia) of the electron transport chain and impaired oxidation of long chain fatty acids by propofol or a propofol metabolite in uniquely susceptible patients (mimics the mitochondrial myopathies). The majority of reported propofol-induced "seizures" during induction of anesthesia or emergence from anesthesia reflect spontaneous excitatory movements of subcortical origin (not thought to be due to cortical epileptic activity). There appears to be no reason to avoid propofol for sedation, induction, and maintenance of anesthesia in patients with known seizures. Intense dreaming activity, amorous behavior, and hallucinations have been reported during recovery from and low-dose infusions of propofol. Propofol strongly supports the growth of Escherichia coli and Pseudomonas aeruginosa. Postoperative surgical infections manifesting as temperature elevations have been attributed to extrinsic contamination of propofol. For this reason, it is recommended that (a) an aseptic technique be used in handling propofol as reflected by disinfecting the ampule neck surface or vial rubber stopper with 70% isopropyl alcohol; (b) the contents of the ampule containing propofol should be withdrawn into a sterile syringe immediately after opening and administered promptly; and (c) the contents of an opened ampule must be discarded if they are not used within 6 hours. Propofol has potent antioxidant properties that resemble those of the endogenous antioxidant vitamin E (neuroprotective effect of propofol). Pain on injection is the most commonly reported adverse event associated with propofol administration to awake patients. Preceding the propofol with 1% lidocaine or prior administration of a potent short-acting opioid decreases the incidence of discomfort experienced by the patient. An oral formulation of etomidate for transmucosal delivery has been shown to produce dose-dependent sedation. Administration through the oral mucosa results in direct systemic absorption while bypassing hepatic metabolism (higher blood concentrations are achieved more rapidly compared with drug that is administered by mouth). The anesthetic effect of etomidate resides predominantly in the R isomer, which is approximately five times as potent as the S isomer. Etomidate is rapidly metabolized by hydrolysis of the ethyl ester side chain to its carboxylic acid ester, resulting in a water-soluble, pharmacologically inactive compound. Involuntary myoclonic movements are common during the induction period as a result of alteration in the balance of inhibitory and excitatory influences on the thalamocortical tract (frequency of this myoclonic-like activity can be attenuated by prior administration of an opioid). The principal limiting factor in the clinical use of etomidate for induction of anesthesia is the ability of this drug to transiently depress adrenocortical function. Suppression of adrenocortical function limits the clinical usefulness for long-term treatment of intracranial hypertension. This characteristic may be used to facilitate localization of seizure foci in patients undergoing cortical resection of epileptogenic tissue. Etomidate also possesses anticonvulsant properties and has been used to terminate status epilepticus. Etomidate has been observed to augment the amplitude of somatosensory evoked potentials, making monitoring of these responses more reliable. Etomidate has been proposed for induction of anesthesia in patients with little or no cardiac reserve. In the majority of patients, etomidate-induced decreases in tidal volume are offset by compensatory increases in the frequency of breathing. Pain on injection and venous irritation has been virtually eliminated with use of etomidate in a lipid emulsion vehicle rather than propylene glycol. These spontaneous movements, particularly myoclonus, occur in 50% to 80% of patients receiving etomidate in the absence of premedication. The mechanism of etomidate-induced myoclonus appears to be disinhibition of subcortical structures that normally suppress extrapyramidal motor activity. Etomidate causes adrenocortical suppression by producing a dose-dependent inhibition of the conversion of cholesterol to cortisol. Conceivably, patients experiencing sepsis or hemorrhage and who might require an intact cortisol response would be at a disadvantage should etomidate be administered. Conversely, suppression of adrenocortical function could be considered desirable from the standpoint of "stress-free" anesthesia. The longer context-sensitive half-time of lorazepam makes this drug an attractive choice to facilitate sedation of patients in critical care environments. Benzodiazepines are unique in the availability of a specific pharmacologic antagonist, flumazenil. Table 5-2 Pharmacologic Effects of Benzodiazepine Anxiolysis Sedation Anticonvulsant actions Spinal cord­mediated muscle relaxation Treat acute insomnia Not adequate for surgical procedures No influence on required dose of neuromuscular blocking drugs Amnestic potency is greater than sedative effect. Fatigue and drowsiness are the most common side effects in patients treated chronically with benzodiazepines. Although effects on ventilation seem to be absent, it may be prudent to avoid these drugs in patients with chronic lung disease characterized by hypoventilation and/or decreased arterial oxygenation as they may interact with other medications to have adverse effects. Acute administration of benzodiazepines may produce transient anterograde amnesia, especially if there is concomitant ingestion of alcohol. Anesthetic requirements for inhaled and injected anesthetics are decreased by benzodiazepines. Although benzodiazepines, especially midazolam, potentiate the ventilatory depressant effects of opioids, the analgesic actions of opioids are reduced by benzodiazepines. Midazolam has replaced diazepam for use in preoperative medication and conscious sedation. The amnestic effects of midazolam are more potent than its sedative effects (patients may be awake but remain amnestic for events and conversations such as postoperative instructions for several hours). Midazolam undergoes rapid absorption from the gastrointestinal tract and prompt passage across the blood­brain barrier. Despite this prompt passage into the brain, midazolam is considered to have a slow effect-site equilibration time (0. The short duration of action of a single dose of midazolam is due to its lipid solubility, leading to rapid redistribution from the brain to inactive tissue sites as well as rapid hepatic clearance. The principal metabolite of midazolam, 1-hydroxymidazolam, has approximately half the activity of the parent compound. Paradoxical excitement occurs in less than 1% of all patients receiving midazolam and is effectively treated with a specific benzodiazepine antagonist, flumazenil. Midazolam produces dose-dependent decreases in ventilation (patients with chronic obstructive pulmonary disease experience even greater Chapter 5 · Intravenous Sedatives and Hypnotics Table 5-3 Comparative Pharmacology of Benzodiazepines Equivalent Dose (mg) Midazolam Diazepam Lorazepam 0. Cardiac output is not altered by midazolam, suggesting that blood pressure changes are due to decreases in systemic vascular resistance. Oral midazolam syrup (2 mg/mL) is Chapter 5 · Intravenous Sedatives and Hypnotics 135 b. The most significant side effect of midazolam when used for sedation is depression of ventilation. Increasing age greatly increases pharmacodynamic variability and is associated with generally increased sensitivity to the hypnotic effects of midazolam. In healthy patients receiving small doses of benzodiazepines, the cardiovascular depression associated with these drugs is minimal. When significant cardiovascular responses occur, it is most likely a reflection of benzodiazepine-induced peripheral vasodilation. Midazolam may be administered to supplement opioids, propofol, and/or inhaled anesthetics during maintenance of anesthesia (anesthetic requirements for volatile anesthetics are decreased in a dose-dependent manner by midazolam). Emergence time from midazolam infusion is increased in elderly patients, obese patients, and in the presence of severe liver disease. Paradoxical vocal cord motion is a cause of nonorganic upper airway obstruction and stridor that may manifest postoperatively (midazolam 0. Diazepam is a highly lipid-soluble benzodiazepine with a more prolonged duration of action compared with midazolam. Because of the beneficial aspects of midazolam pharmacology, parenteral diazepam is seldom used as part of current anesthetic regimens (see Table 5-3). Oxazepam is a pharmacologically active metabolite of diazepam (duration of action is slightly shorter than that of diazepam because oxazepam is converted to pharmacologically inactive metabolites). Alprazolam has significant anxiety-reducing effects in patients with primary anxiety and panic attacks (may be an alternative to midazolam for preoperative medication). Clonazepam is a highly lipid-soluble benzodiazepine that is well absorbed after oral administration and is particularly effective in the control and prevention of seizures, especially myoclonic and infantile spasms. Flurazepam is used exclusively to treat insomnia (30 mg orally to adults produces a hypnotic effect in 15 to 25 minutes and lasts 7 to 8 hours). Temazepam is an orally active benzodiazepine administered exclusively for the treatment of insomnia. Triazolam is an orally absorbed benzodiazepine that is effective in the treatment of insomnia. Marked anterograde amnesia has developed when this drug has been selfadministered in attempts to facilitate sleep when traveling through several time zones. Flumazenil is a specific and exclusive benzodiazepine antagonist with a high affinity for benzodiazepine receptors, where it exerts minimal agonist activity (prevents or reverses, in a dose-dependent manner, all the agonist effects of benzodiazepines). The dose of flumazenil should be titrated individually to obtain the desired level of consciousness. The duration of action of flumazenil is 30 to 60 minutes, and supplemental doses of the antagonist may be needed to maintain the desired level of consciousness. An alternative to repeated doses of flumazenil to maintain wakefulness is a continuous low-dose infusion of flumazenil, 0. The administration of flumazenil to patients being treated with antiepileptic drugs for control of seizure activity is not recommended as it could precipitate acute withdrawal seizures. Flumazenil-induced antagonism of excess benzodiazepine agonist effects is not followed by acute anxiety, hypertension, tachycardia, or neuroendocrine evidence of a stress response in postoperative patients. The introduction of thiopental in 1934 revolutionized the practice of anesthesia by making it possible to induce general anesthesia in seconds, avoiding a slow, often unpleasant, more dangerous induction with diethyl ether. Varying degrees of hypertonus and purposeful skeletal muscle movements often occur independently of surgical stimulation. The frequency of emergence delirium limits the clinical usefulness of ketamine as a sole agent. The racemic form of ketamine has been the most frequently used preparation although S-ketamine is clinically available (produces more intense analgesia, more rapid metabolism and thus recovery, less salivation, and a lower incidence of emergence reactions than R[]-ketamine).

Zinc is an enzymatic cofactor essential for cell growth and the synthesis of nucleic acid erectile dysfunction aafp cheap vivanza 20 mg mastercard, carbohydrates erectile dysfunction drugs in canada buy vivanza 20 mg low price, and proteins erectile dysfunction medication online buy vivanza with a visa. Epinephrine is a circulating hormone synthesized erectile dysfunction treatment without medication generic vivanza 20 mg buy line, stored impotence 10 20 mg vivanza buy, and released from the adrenal medulla. Its natural functions upon release into the circulation include regulation of myocardial contractility, heart rate, vascular and bronchial smooth muscle tone, glandular secretions, and metabolic processes such as glycogenolysis and lipolysis. It is a potent activator of -adrenergic receptors and also activates 1 and 2 receptors. Epinephrine is poorly lipid soluble, preventing its ready entrance into the central nervous system and accounting for the lack of cerebral effects. Clinical uses of epinephrine include treatment of life-threatening allergic reactions/anaphylaxis, treatment of severe asthma and bronchospasm, administration during cardiopulmonary resuscitation as a vital therapeutic drug, administration during periods of hemodynamic instability to promote myocardial contractility and increase vascular resistance, and continuous infusion for continuous support of myocardial contractility and vascular resistance. Epinephrine is added to local anesthetic solutions to decrease systemic absorption prolonging the duration of action of the anesthetic for regional and local anesthesia. The cardiovascular effects of epinephrine result from stimulation of - and adrenergic receptors (see Table 18-1). Smooth muscles of the bronchi are relaxed by epinephrine-induced activation of 2 receptors. The bronchodilating effects of epinephrine are not seen in the presence of -adrenergic blockade. Epinephrine has the most significant effect on metabolism of all the catecholamines. Release of endogenous epinephrine and the resulting glycogenolysis and inhibition of insulin secretion is the most likely explanation for perioperative hyperglycemia. Selective 2-adrenergic agonist effects of epinephrine are speculated to reflect activation of the sodiumpotassium pump in skeletal muscles, leading to a transfer of potassium ions into cells. The observation that serum potassium measurements in blood samples obtained immediately before induction of anesthesia are lower than measurements 1 to 3 days preoperatively is presumed to reflect stress-induced release of epinephrine. In making therapeutic decisions based on a preinduction serum potassium measurement, especially in patients without a reason to experience hypokalemia, one should consider the possible role of preoperative anxiety and the release of epinephrine. Epinephrine causes contraction of the radial muscles of the iris, producing mydriasis. Epinephrine, norepinephrine, and isoproterenol produce relaxation of gastrointestinal smooth muscle. Activation of -adrenergic receptors relaxes the detrusor muscle of the bladder, whereas activation of -adrenergic receptors contracts the trigone and sphincter muscles. Hepatosplanchnic vasoconstriction occurs as well as impaired renal blood flow as cardiac output is diverted to the dilated skeletal muscle vasculature. Norepinephrine is the endogenous neurotransmitter synthesized and stored in postganglionic sympathetic nerve endings and released with sympathetic nerve stimulation. A continuous infusion of norepinephrine, 2 to 16 g per minute, may be used to treat refractory hypotension. The primary utility of norepinephrine is as a potent vasoconstrictor to increase total peripheral vascular resistance and mean arterial pressure. It is a first-line agent in the treatment of refractory hypotension during severe sepsis. Norepinephrine-induced vasoconstriction and redistribution of flow may increase splanchnic blood flow and urine output in severely hypotensive septic patients. Excessive vasoconstriction and decreased perfusion of renal, splanchnic, and peripheral vascular beds may lead to end-organ hypoperfusion and ischemia. Dopamine is an endogenous catecholamine that regulates cardiac, vascular, and endocrine function and is an important neurotransmitter in the central and peripheral nervous systems. Dopamine receptors may also be associated with the neural mechanism for "reward" that is associated with cocaine and alcohol dependence. Traditionally, the pharmacokinetics of dopamine has been attributed to dose-dependent effects on varying receptors (too simplistic as even in healthy individuals there are a wide range of clinical responses depending on individual variability in pharmacokinetics). The effects of dopamine cannot be predicted based on the dose, and the drug must be titrated to effect. Dopamine increases cardiac output by stimulation of 1 receptors, increasing stroke volume (less dysrhythmogenic than epinephrine). Rapid metabolism of dopamine with an elimination half-life of 1 to 2 minutes mandates its use as a continuous infusion (1 to 20 g/kg/ minute) to maintain therapeutic plasma concentrations. Dopamine is used clinically to increase cardiac output in patients with decreased contractility, low Chapter 18 · Sympathomimetic Drugs 359 2. The divergent pharmacologic effects of dopamine and dobutamine make their use in combination potentially useful (infusions of dopamine and dobutamine produce a greater improvement in cardiac output, at lower doses, than can be achieved by either drug alone). The objective of combination therapy is to increase coronary perfusion and cardiac output while decreasing afterload, similar to an intraaortic balloon pump. The term renal-dose dopamine or low-dose dopamine refers to the continuous infusion of small doses (1 to 3 g/kg/minute) of dopamine to patients to promote renal blood flow. In healthy individuals, low-dose dopamine increases renal blood flow and induces natriuresis and diuresis. In the absence of data confirming the efficacy of dopamine in preventing acute renal failure, renal-dose dopamine cannot be recommended. Dopamine is associated more than dobutamine or epinephrine with dose-related sinus tachycardia and the potential to cause ventricular arrhythmias and may predispose to myocardial ischemia by precipitating tachycardia, increasing contractility, increasing afterload, and precipitating coronary artery vasospasm. There is no evidence that low-dose dopamine has beneficial effects on splanchnic function or reduces the progression to multiorgan failure in sepsis. Dopamine disrupts metabolic and immunologic functions through its effects on hormones and lymphocyte function. In the acute phase of an illness, dopamine induces the pattern of hypopituitarism seen in prolonged critical illness and chronic stress. The infusion of low-dose dopamine interferes with the ventilatory response to arterial hypoxemia and hypercapnia, reflecting the role of dopamine as an inhibitory neurotransmitter at the carotid bodies (result is depression of ventilation in patients who are being treated with dopamine to increase myocardial contractility). Isoproterenol is the most potent activator of all the sympathomimetics with 1 and 2 receptor activity (two to three times more potent than epinephrine and at least 100 times more active than norepinephrine, devoid of agonist effects). The cardiovascular effects of isoproterenol reflect activation of 1 receptors in the heart and 2 receptors in skeletal muscle. Although cardiac output may increase thereby increasing systolic blood pressure, the mean arterial pressure may decrease due to decreases in systemic vascular resistance and associated decreases in diastolic blood pressure. Compensatory baroreceptor-mediated reflex slowing of the heart rate does not occur during infusion of isoproterenol because mean arterial pressure is not increased. Metabolism of isoproterenol in the liver by catechol-O-methyltransferase is rapid, necessitating a continuous infusion to maintain therapeutic plasma concentrations. A continuous infusion of isoproterenol, 1 to 5 g per minute, is effective in increasing the heart rate in adults in the presence of heart block. Isoproterenol is used to provide sustained increases in heart rate before insertion of a temporary or permanent cardiac pacemaker. The combination of decreased diastolic blood pressure and increased heart rate and dysrhythmias may lead to myocardial ischemia. Dobutamine is a synthetic catecholamine derived from isoproterenol consisting of a 50:50 racemic mixture of two Chapter 18 · Sympathomimetic Drugs 361 stereoisomers. Unlike dopamine, dobutamine does not act indirectly by stimulating the release of endogenous norepinephrine. Renal blood flow, however, may improve as a result of drug-induced increases in cardiac output. Rapid metabolism of dobutamine (half-life of 2 minutes) necessitates its administration as a continuous infusion of 2 to 10 g/kg/minute to maintain therapeutic plasma concentrations. Dobutamine is used to improve cardiac output in patients with congestive heart failure and is also useful for weaning from cardiopulmonary bypass. Vasodilators may be combined with dobutamine or dopamine to decrease afterload, optimizing cardiac output in the presence of increased systemic vascular resistance. The use of dobutamine may be limited by the occurrence of tachyarrhythmias (occur more frequently at higher dosages or in patients with underlying arrhythmias or heart failure). Ephedrine is an indirect (stimulation of release of endogenous norepinephrine) and direct (stimulates - and -adrenergic receptors) acting synthetic sympathomimetic. Until recently, ephedrine was considered the preferred sympathomimetic for administration to parturients experiencing decreased systemic blood pressure owing to spinal or epidural anesthesia. Recent reviews of trials of ephedrine versus phenylephrine have concluded that systemic blood pressure control is similar with both drugs but phenylephrine is associated with a higher umbilical artery pH at delivery than ephedrine (seems that agonists such as phenylephrine may be preferable to ephedrine for treatment of maternal hypotension). Cardiovascular effects of ephedrine resemble those of epinephrine, but its systemic blood pressure­elevating response is less intense and lasts approximately 10 times longer. The principal mechanism for cardiovascular effects produced by ephedrine is increased myocardial contractility due to activation of 1 receptors. In the presence of preexisting -adrenergic blockade, the cardiovascular effects of ephedrine may resemble Chapter 18 · Sympathomimetic Drugs 363 responses more typical of -adrenergic receptor stimulation. A second dose of ephedrine produces a less intense systemic blood pressure response than the first dose (tachyphylaxis, occurs with many sympathomimetics). Phenylephrine mimics the effects of norepinephrine but is less potent and longer lasting (principally stimulates 1-adrenergic receptors by a direct effect, with only a small part of the pharmacologic response being indirect-acting due to its ability to evoke the release of norepinephrine). The dose of phenylephrine necessary to stimulate 1 receptors is far less than the dose that stimulates 2 receptors. Phenylephrine primarily causes venoconstriction rather than arterial constriction. Phenylephrine is believed to be particularly useful in patients with coronary artery disease and in patients with aortic stenosis because it increases coronary perfusion pressure without chronotropic side effects, unlike most other sympathomimetics. The reflex vagal effects produced by phenylephrine can be used to slow heart rate in the presence of hemodynamically significant supraventricular tachydysrhythmias. Topically applied, phenylephrine is a widely available nasal decongestant (brand name Neo-Synephrine). Time course and hemodynamic effects of alpha-1adrenergic bolus administration in anesthetized patients with myocardial disease. Stimulation of receptors by a continuous infusion of phenylephrine during acute potassium loading interferes with the movement of potassium ions across cell membranes into cells. Administration of phenylephrine in the absence of an acute potassium load does not change the plasma potassium concentration. Systemic manifestations of sympathetic nervous system activation (systemic hypertension, tachycardia, baroreceptor-mediated bradycardia) may accompany vascular absorption of agonists (phenylephrine, epinephrine) when used as topical or injected vasoconstrictors in the surgical field. Systemic hypertension induced by intravenously administered agonists may not require treatment. Severe hypertension may require pharmacologic interventions but treatment must not decrease the ability of the stressed myocardium to increase contractility and heart rate (vasodilating drugs such as nitroprusside or nitroglycerin are indicated). Selective 2-adrenergic agonists relax bronchiole and uterine smooth muscle but, in contrast to isoproterenol, generally lack stimulating (1) effects on the heart (Table 18-2). With optimal inhalation technique (discharge the inhaler while taking a slow deep breath over 5 to 6 seconds, and then hold the breath at full inspiration for 10 seconds), approximately 12% of the drug is delivered from the metered-dose inhaler to the lungs; the remainder is deposited in the mouth, pharynx, and larynx. The presence of an endotracheal tube decreases by approximately 50% to 70% the amount of drug delivered by a metered-dose inhaler that reaches the trachea. Actuation of the metered-dose inhaler during a mechanically delivered inspiration increases the amount of drug that passes beyond the distal end of the tracheal tube. The widespread distribution of 2-adrenergic receptors makes it likely that undesired responses may result when 2-adrenergic agonists undergo systemic absorption. The principal side effect in awake subjects of 2adrenergic agonists treatment is tremor (caused by direct stimulation of 2 receptors in skeletal muscles). In patients with acute, severe asthma, 2-adrenergic agonists may cause a transient decrease in arterial oxygenation presumed to reflect relaxation of compensatory vasoconstriction in areas of decreased ventilation (supplemental oxygen indicated). Increased mortality in patients with severe asthma treated with 2-adrenergic agonists is most likely a reflection of the severity of the asthma rather than a toxic effect of the drug therapy. Acute metabolic responses to 2-adrenergic agonists include hyperglycemia, hypokalemia, and hypomagnesemia. Albuterol (known as salbutamol outside the United States), is the preferred selective 2-adrenergic agonist for the treatment of acute bronchospasm due to asthma. Administration is most often by metered-dose inhaler, producing about 100 g per puff; the usual dose is two Chapter 18 · Sympathomimetic Drugs 369 puffs delivered during deep inhalations 1 to 5 minutes apart. The duration of action of an inhaled dose is about 4 hours, but significant relief of symptoms may persist up to 8 hours. The effects of albuterol and volatile anesthetics on bronchomotor tone are additive. Terbutaline is a predominantly 2-adrenergic agonist that may be administered orally, subcutaneously, or by inhalation to treat asthma. Digoxin is used most often during the perioperative period for the management of supraventricular tachydysrhythmias. Digoxin may be selected only for treatment of symptoms that persist after administration of angiotensin-converting enzyme inhibitors or -adrenergic antagonists. Direct current cardioversion in the presence of digoxin may be hazardous because of increased risk for developing cardiac dysrhythmias, including ventricular fibrillation. In approximately 30% of patients with Wolff-ParkinsonWhite syndrome, digitalis decreases refractoriness in the accessory conduction pathway to the point that rapid atrial impulses can cause ventricular fibrillation. Digoxin may be harmful in patients with hypertrophic subaortic stenosis because increased myocardial contractility intensifies the resistance to ventricular ejection. Cardiac glycosides have a narrow therapeutic range (estimated that approximately 20% of patients who are being treated with cardiac glycosides experience some form of digitalis toxicity). The most frequent cause of digitalis toxicity in the absence of renal dysfunction is the concurrent administration of diuretics that cause potassium depletion. Hypokalemia probably increases myocardial binding of cardiac glycosides, resulting in an excess drug effect. Digoxin is often administered in situations where digitalis toxicity is difficult to distinguish from the effects of the cardiac disease.

It courses back around the articular pillar of the third cervical vertebra erectile dysfunction doctor in kuwait order vivanza 20 mg with amex, medial to the posterior intertransverse muscle erectile dysfunction treatment medscape vivanza 20 mg purchase line, and divides into medial and lateral branches erectile dysfunction tools discount vivanza 20 mg otc. Its medial branch runs between spinalis capitis and semispinalis cervicis and pierces splenius and trapezius to end in the skin erectile dysfunction guidelines 2014 20 mg vivanza overnight delivery. Deep to trapezius it gives rise to a branch erectile dysfunction kya hota hai purchase discount vivanza line, the third occipital nerve, that pierces trapezius and ends in the skin of the lower occipital region, medial to the greater occipital nerve and connected to it. The dorsal ramus of the suboccipital nerve and medial branches of the dorsal rami of the second and third cervical nerves are sometimes joined by loops to form the posterior cervical plexus. The dorsal rami of the lower five cervical nerves curve back around the vertebral articular pillars and divide into medial and lateral branches. Medial branches of the fourth and fifth cervical nerves run between semispinalis cervicis and semispinalis capitis, reach the vertebral spines and pierce splenius and trapezius to end in the skin. The medial branches of the lowest three cervical nerves are small and end in semispinalis cervicis, semispinalis capitis, multifidus and interspinales. The lateral branches supply iliocostalis cervicis, longissimus cervicis and longissimus capitis. Thoracic dorsal spinal rami - Thoracic dorsal rami pass backward close to the vertebral facet joints to divide into medial and lateral branches. Each medial branch emerges between a joint and the medial edges of the superior costotransverse ligament and intertransverse muscle. Each lateral branch runs in the interval between the ligament and the muscle before inclining posteriorly on the medial side of levator costae. Medial branches of the upper six thoracic dorsal rami pass between and supply semispinalis thoracis and multifidus, then pierce rhomboids and trapezius and reach the skin near the vertebral spines. Medial branches of the lower six thoracic dorsal rami mainly supply multifidus and longissimus thoracis and occasionally the skin in the median region. Lateral branches increase inferiorly in size and run through, or deep to , longissimus thoracis to the interval between it and iliocostalis cervicis, supplying these muscles and levatores costarum. The lower five or six also have cutaneous branches and pierce serratus posterior inferior and latissimus dorsi in line with the costal angles. The twelfth thoracic lateral branch sends a filament medially along the iliac crest, then passes down to the anterior gluteal skin. Medial cutaneous branches of the thoracic dorsal rami descend close to the vertebral spines before reaching the skin; lateral branches descend across as many as four ribs before becoming superficial. The branch of the twelfth thoracic reaches the skin a little above the iliac crest. Lumbar dorsal spinal rami - Lumbar dorsal rami pass back, medial to the medial intertransverse muscles, and divide into medial and lateral branches. They are related to the bone between the accessory and mammillary processes and may groove it, crossing a distinct notch or even a foramen. In addition, the upper three rami give rise to cutaneous nerves that pierce the aponeurosis of latissimus dorsi at the lateral border of erector spinae and cross the iliac crest posteriorly to reach the gluteal skin, some extending as far as the level of the greater trochanter. The upper three are covered at their exit by multifidus and divide into medial and lateral branches. Lateral branches join together and with lateral branches of the last lumbar and fourth sacral dorsal rami, forming loops dorsal to the sacrum. Branches from these loops run dorsal to the sacrotuberous ligament and form a second series of loops under gluteus maximus. From these, two or three gluteal branches pierce the gluteus maximus (along a line from the posterior superior iliac spine to the coccygeal apex) to supply the posterior gluteal skin. The dorsal rami of the fourth and fifth sacral nerves are small and lie below multifidus. They unite with each other and with the coccygeal dorsal ramus to form loops dorsal to the sacrum; filaments from these supply the skin over the coccyx. Coccygeal dorsal spinal ramus - the coccygeal dorsal spinal ramus does not divide into medial and lateral branches. Typically, dermatomes extend around the body from the posterior to the anterior median line. The upper half of each zone is supplemented by the nerve above, and the lower half by the nerve below. The area supplied by dorsal rami is limited laterally by the dorsolateral line, which descends laterally from the occiput to the medial end of the acromion, continues to the posterior aspect of the greater trochanter and curves medially to the coccyx. Cutaneous strips supplied by dorsal rami do not correspond exactly to those served by ventral rami and differ in both breadth and position. Dermatomes of adjacent spinal nerves overlap markedly, particularly in the segments least affected by development of the limbs. When the second thoracic spinal ramus is severed, anaesthesia is sharply demarcated, but some overlap for awareness of painful and thermal stimuli may exist. Hence, the area of total anaesthesia and analgesia following section of peripheral nerves is always less than might be anticipated from their anatomical distribution. C2 C2 C3 C4 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 C8 C6 C7 L2 L1 S3 S4 C3 C4 T2 T4 T6 T8 T10 T12 T3 T5 T7 T9 T11 L1 L2 C8 T1 C7 T2 C5 C2 C3 C4 C5 C6 C7 T1 T2 C5 T1 C6 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 L3 L3 L4 L5 L4 L5 S1 S1 L5. The small diagram shows the regular arrangement of dermatomes in the upper and lower limbs of the embryo. The dimensions and relative volumes of white matter and centrally aggregated neurone cell bodies vary according to the level. The amount of grey matter at any level is a function of the amount of muscle, skin and other tissues innervated by neurones at that level. It is therefore largest by proportion in the cervical and lumbar enlargements, because neurones in these segments of the cord innervate the limbs; it is attenuated at thoracic levels. The absolute amount of white matter is greatest at cervical levels and decreases progressively at lower levels; this is the case because descending tracts shed fibres as they descend, and ascending tracts accumulate fibres as they ascend. In the centre of the spinal grey matter, the central canal extends the whole length of the spinal cord. Rostrally, the central canal extends into the caudal half of the medulla oblongata, where it opens into the fourth ventricle. The grey matter that immediately surrounds the central canal and unites the two sides is termed the dorsal and ventral grey commissure. The dorsal horns are the site of termination of primary afferent fibres, which enter via the dorsal roots of spinal nerves. The dorsal horn may be described in terms of a head, neck and base, the individual constituents of which are described in more detail later. The ventral horns contain efferent neurones whose axons leave the spinal cord in ventral nerve roots. A small intermediate lateral horn is present at the thoracic and upper lumbar levels and contains the cell bodies of preganglionic sympathetic neurones. Spinal grey matter is a complex mixture of neuronal cell bodies (somata), their processes (neurites) and synaptic connections, neuroglia and blood vessels. Neurones in the grey matter are multipolar and vary in size and other features, particularly the length and arrangement of their axons and dendrites. Axons of Golgi type I neurones pass out of the grey matter into ventral spinal roots or spinal tracts. The distribution of neurones may be intrasegmental- deployed within a single segment-or intersegmental-spread through several segments. Viewed from the perspective of its longitudinal columnar organization, the grey matter of the spinal cord consists of a series of discontinuous cell groupings associated with their corresponding segmentally arranged spinal nerves. Many complex polysynaptic reflex paths (ipsilateral, contralateral, intrasegmental and intersegmental) start from this region, and many long ascending tract fibres that pass to higher levels arise from it. Lamina I (lamina marginalis) is a very thin layer with an ill-defined boundary at the dorsolateral tip of the dorsal horn. It has a reticular appearance, reflecting its content of intermingling bundles of coarse and fine nerve fibres. It contains small, intermediate and large neuronal somata, many of which are fusiform in shape. Some workers believe that the Sixth thoracic Third lumbar Neuronal Cell Groups of the Spinal Cord Second sacral. Note the changes in overall profile and the relative changes in grey and white regions, their shapes, sizes and proportions (magnification ×5). A Dorsolateral fasciculus (of Lissauer) Fasciculus interfascicularis Fasciculus gracilis Fasciculus cuneatus Dorsal spinocerebellar tract Dorsal fasciculus proprius lower extremity Lateral corticospinal tract: trunk upper extremity Denticulate ligament Ventral white commissure Medial longitudinal fasciculus Medial reticulospinal tract Medial tectospinal tract Spino-olivary tract Ventrolateral vestibulospinal tract Ventral reticulospinal tract Sulcomarginal fasciculus Lateral reticulospinal tract Rubrospinal tract Ventral spinocerebellar tract Lateral spinothalamic and spinotectal tracts Ventrolateral reticulospinal tract Ventral spinothalamic tract Ventral fasciculus proprius Ventral corticospinal tract B Dorsolateral fasciculus (of Lissauer) Lateral corticospinal tract Tegmentospinal tract Lateral reticulospinal tract Fasciculus septomarginalis Dorsal fasciculus proprius Fasciculus gracilis Lateral fasciculus proprius Ventral spinocerebellar tract Medial reticulospinal tract Ventrolateral vestibulospinal tract Ventral reticulospinal tract Ventral spinothalamic tract Ventral corticospinal tract Sulcomarginal fasciculus Lateral spinothalamic and spinotectal tracts Spino-olivary tract Ventral fasciculus proprius. Its neuronal somata vary considerably in size and shape: small and round, intermediate and triangular, very large and stellate. Both have a mixed cell population, but the former contains many prominent well-staining somata interlaced by numerous bundles of transverse, dorsoventral and longitudinal fibres. It has a densely staining medial third of small, densely packed neurones and a lateral two-thirds containing larger, more loosely packed, triangular or stellate somata. Its medial part has numerous propriospinal reflex connections with the adjacent grey matter and segments concerned with both movement and autonomic functions. Its neurones display a heterogeneous mixture of sizes and shapes from small to moderately large. The axons from these interneurones influence motor neurones bilaterally, perhaps directly but more probably by excitation of small neurones supplying -efferent fibres to muscle spindles. The large motor neurones supply motor end-plates of extrafusal muscle fibres in striated muscle. The former have a lower rate of firing and lower conduction velocity and tend to innervate type S muscle units. The smaller motor neurones give rise to small-diameter efferent axons (fusimotor fibres), which innervate the intrafusal muscle fibres in muscle spindles. Lamina X surrounds the central canal and consists of the dorsal and ventral grey commissures. The dorsal horn is a major receptive zone (zone of termination) of primary afferent fibres, which enter the spinal cord through the dorsal roots of spinal nerves. Dorsal root fibres contain numerous molecules that are either known or suspected to fulfill a neurotransmitter or neuromodulator role. The larger motor neurones in the ventral grey column are visibly grouped (cresyl fast violet stain). This is a poorly understood disorder that may be caused by a gradual dropout of motor units or muscle fibres as a result of aging superimposed on residual anterior horn cells that were previously depleted as a result of the original poliomyelitis. Increased metabolic demand on the maximally reinnervated motor units may also play a significant role. At age 4 years he had acute poliomyelitis, characterized by profound weakness of both lower extremities and less severe weakness of the upper extremities. Upper extremity strength improved significantly thereafter, but he had persistent weakness in the lower extremities, which gradually improved. After 2 years he continued to exhibit weakness and significant atrophy of all muscles in the right lower extremity, particularly the gastrocnemius. He was unchanged thereafter until age 60, when he began to experience increased weakness in the lower extremities, particularly on the right side, ultimately necessitating the use of a leg brace. He also complains of pain in the right lower extremity, especially in the knee and ankle, and notes global fatigue. Neurological examination demonstrates mild weakness in the left lower extremity and marked weakness of all muscle groups in the right lower extremity, particularly the dorsiflexors and plantar flexors of the right foot. An electromyogram with a nerve conduction study of the lower extremities shows denervation in all muscles tested. Phagocytic neuronophagic (microglial) clusters mark the site of dying motor neurones. He has noted increasing difficulty jogging and has had several falls as a result of catching his foot on a curb. He also reports deterioration in his penmanship and trouble typing on his computer keyboard. He denies symptoms referable to bulbar function and has experienced no sphincter disturbances. Pathologically, degeneration is observed primarily in the anterior horns of the spinal cord, in motor cranial nerve nuclei, and in the lateral corticospinal tracts. Although it begins at spinal levels, the disease generally spreads to involve motor cranial nerve nuclei, with resultant dysarthria, dysphagia and impaired respiratory function. Cross-section stained for myelin sheaths demonstrates degeneration of the lateral (corticospinal) pathways (arrows); less marked changes reflect loss of recurrent anterior horn cell collateral fibres. Kubik Laboratory of Neuropathology, Massachusetts General Hospital, Tessa Hedley-White, Director. Most if not all primary afferent fibres divide into ascending and descending branches on entering the cord. These then travel for variable distances in the tract of Lissauer, near the surface of the cord, and send collaterals into the subjacent grey matter. The formation, topography and division of dorsal spinal roots have all been confirmed in humans. At the dorsolateral tip of the dorsal horn, deep to the tract of Lissauer, lies a thin lamina of neurones, the lamina marginalis. It receives afferents via the dorsal roots and is the site of origin of the spinothalamic tract complex. These propriospinal neurones link segments for the mediation of intraspinal coordination. In the human spinal cord, it can usually be identified from the eighth cervical to the third or fourth lumbar segments. Some send axons into the dorsal spinocerebellar tracts, and others are interneurones.

Buy generic vivanza 20 mg on-line. Causes and Cures for Erectile Dysfunction.

References